含纤维断裂复合材料热阻变化的细观建模

为探讨单向纤维增强复合材料中纤维损伤与材料热阻变化之间的关系,建立了由纤维断裂引起热阻变化的细观理论模型,并利用该模型对热阻变化率进行了定性分析。针对纵向传热与垂直传热两种情形下的热阻进行分析,结合Weibull纤维强度分布模型,引入纤维失效长度作为纤维链段的最小长度,获得了纤维断裂引起的复合材料纵向和沿厚度方向热阻变化率的解析函数。采用Monte-Carlo随机方法对外加应力作用下复合材料热阻随着纤维断裂而发生变化的过程进行模拟。研究结果表明:无论是纵向热阻还是厚度方向的热阻,热阻变化率均随纤维断点数目的增大而线性递增;纤维体积组分越大,热阻变化率越大。纵向热阻变化率随着纤维/基体导热系数比β的增大而迅速增大,但当β10时增大的幅度逐渐减弱;而厚度方向的热阻变化率则随着β的增大先急剧增大而后递减,当纤维与基体的导热系数相当时(在β=1附近)达到最大值。

Micro-modeling of thermal resistance change in fibers reinforced composites with fiber breakage

A micro-model of thermal resistance change with fiber breakage was developed to describe the correla-tion between the thermal resistance change and the fiber damage in unidirectional fibers reinforced composites,and a qualitative analysis of the thermal resistance change was carried out based on the present model.Heat transfers in longitudinal and thickness directions of the composite were both analyzed.Analytical solutions were derived for the thermal resistance change in both longitudinal and thickness directions of the composite by the standard Weibull model in combination with the failure length of fibers as the minimum length of the fiber segments.The process of fiber break under applied tensile stress was simulated with Monte-Carlo random method,during which the thermal resistance change in the composite was calculated simultaneously.The results of the present study show that the thermal resistance changes in both the longitudinal and thickness directions increase linearly with the number of fiber breakage in the composite.For larger fiber volume fraction,the thermal resistance changes more greatly.The ther-mal resistance change in longitudinal direction of the composite increases greatly by the fiber/matrix thermal conduc-tivity ratioβ,but the increase amplitude reduces gradually while the fiber/matrix thermal conductivity ratio greater than 10 (i.e.β>10).However,the thermal resistance change in thickness direction increases dramatically from the beginning and then decreases with the increase of the fiber/matrix thermal conductivity ratioβ,and the maximum value of the thermal resistance change occurs for the fiber thermal conductivity close to that of the matrix (i.e. aroundβ=1).